1. Field
The present invention relates to a light emitting device and a lighting system.
2. Background
A light emitting diode (LED) is a semiconductor element for converting electric energy into light. As compared with existing light sources such as a fluorescent lamp and an incandescent electric lamp and so on, the LED has advantages of low power consumption, a semi-permanent span of life, a rapid response speed, safety and an environment-friendliness. For this reason, many researches are devoted to substitution of the existing light sources with the LED. The LED is now increasingly used as a light source for lighting devices, for example, various lamps used interiorly and exteriorly, a liquid crystal display device, an electric sign and a street lamp and the like.
FIGS. 1 and 2 are cross sectional views showing the schematic configurations of prior vertical type light emitting devices.
First, referring to FIG. 1, a prior light emitting device 100 includes a substrate 110, a p-type conductive layer 120, a p-type semiconductor layer 130, an active layer 140, an n-type semiconductor layer 150 and an n-type electrode pad 160.
Regarding the light emitting device 100 shown in FIG. 1, light which is generated from the active layer 140 and is outward emitted is partially blocked by the uppermost n-type electrode pad 160. Therefore, the light emitting device 100 has low light emission efficiency.
Next, referring to FIG. 2, a prior light emitting device 200 includes a substrate 210, an n-type conductive layer 220, an insulation layer 230, a p-type conductive layer 240, a p-type semiconductor layer 250, an active layer 260, an n-type semiconductor layer 270 and an n-type electrode pad 241. The n-type conductive layer 220 includes conductive vias 220a, 220b and 220c penetrating the p-type conductive layer 240, the p-type semiconductor layer 250 and the active layer 260 and contacting with the n-type semiconductor layer 270.
Unlike the light emitting device 100 shown in FIG. 1, the upper portion of the light emitting device 200 shown in FIG. 2 is not blocked by an electrode, so that the light emitting device 200 has light-extraction efficiency higher than that of a prior light emitting device.
However, the insulation layer 230 is formed in the areas of the conductive vias 220a, 220b and 220c, which project into the n-type semiconductor layer 270. This causes a contact area between the n-type conductive layer 220 and the n-type semiconductor layer 270 to be decreased. The sloping surfaces of the conductive vias 220a, 220b and 220c increase with the increases of the depths of the conductive vias 220a, 220b and 220c, so that a contact area between the n-type semiconductor layer 270 and the conductive vias 220a, 220b and 220c is reduced. For this reason, the prior light emitting device having a via electrode shape has limited light-extraction efficiency.